CONTACT MATERIAL
The contact materials used will define the life you can expect.
- Carbon puck elastomer: 3 million cycles typical
- Printed carbon elastomer: 1 million cycles typical
- Printed silver membrane: 3 million cycles typical
Typically a carbon or gold/nickel plate over copper is recommended if the circuitry is on a printed circuit board. The carbon will have a higher contact resistance with improved immunity to extremely corrosive environments.
Contact Type |
Resistance (ohms) |
Recommended Circuit Board Contact Pattern |
Printed carbon elastomer |
1000 |
|
Carbon puck elastomer |
200 |
Printed silver membrane |
10 as a shorting pad 100 as a full switch | |
LEGENDS
Silk screen legend life will vary depending on key shape, style of the legend, and operating conditions. As a general guideline, a standard printed legend will meet 250,000 to 500,000 finger actuations (as simulated with a rubber test finger) before showing signs of wear.
To increase cycle life, overcoats can be added. This can increase the life to the equivalent of 1 million finger actuations.
Legend colors are typically matched to Pantone Colors with a tolerance of 1 shade. There are printing limitations on the distance between the legend and key edge:
- Silk screen printing: 3mm minimum from key edge
- Convex surface: 20mm minimum keytop radius
- Concave surface: 30mm minimum keytop radius
TACTILE
Sharp tactile feel occurs with the right combination of actuation force, stroke, and rubber hardness. Sharp tactile can be obtained with 60 durometer silicone and a long stroke but as these factors are increased, keypad life decreases.
Using a half membrane switch or full membrane switch with a Metal or Poly Dome for tactile feedback, can provide sharp tactile feel while allowing for a lower overall profile than if the elastomer was designed to provide the tactile feedback.
DIMENSIONS
The following dimensions will be required to design a custom rubber keypad:
- Overall Keypad Length and Width
- Key to Key Center X and Y Axes
- Key Height
- Keytop Length and Width
- Mat/Base Thickness
ELASTOMERIC KEYPAD STANDARD TOLERANCES